In a vast manufactory of steel cars, of steel structural forms, steam has to be conveyed long distances from the boilers. Here, as in similar huge establishments, or in the heating of towns and cities from central stations, it is desirable to lose as little heat as possible by the way, for undue waste means enormous inroads upon profits. There are other reasons for wishing to keep heat within a steam pipe; much damage may be done to fruit, flour and other merchandise unduly warmed. Furthermore there is a risk of setting fire to woodwork, paper, cotton and the like; it has been observed that after a month’s exposure to heat from steampipes, wood takes fire at a temperature which at first would not have led to ignition, because then the wood contained a little moisture. To guard against loss and danger it has long been the practice to cover steampipes with jackets of non-conducting material, such as mineral-wool,--furnace-slag blown into short glassy fibres by a sharp blast of air. Felt, loosely folded, also serves well. Many advertised claims for asbestos are not well founded; this mineral is incombustible and is therefore useful in thick curtains to separate a stage from the auditorium of a theatre. But it is a fairly good conductor, and for steampipes should be used as a direct covering of the metal simply to keep an outer and much thicker coat of felt from being charred. Whatever the material chiefly employed, one point is clearly brought out by experiment, namely, that the air detained by the fibres of a covering greatly aids in obstructing the passage of heat. Hence it is well to keep the materials from becoming compacted together, as do ashes when moistened. Asbestos fibres, which are smooth and glassy, do not take hold of air as do cork and wool. Professor J. M. Ordway, of the Massachusetts Institute of Technology, Boston, tells us that non-conductors should be of materials that are abundant and cheap; clean and inodorous; light and easy to apply; not liable to become compacted by jarring or to change by long keeping; not attractive to insects or mice; not likely to scorch, char or ignite at the long-continued highest temperature to which they may be exposed; not liable to spontaneous combustion when partly soaked in oil; not prone to attract moisture from the air; not capable of exerting chemical action on the surfaces they touch. No material combines all these desirable qualities, but a considerable range of substances fulfil most of the requirements. Tests of steam-pipe coverings at Sibley College, Cornell University, and at Michigan University, have resulted as follows:-- Relative Amount Kind of Covering of Heat Transmitted